Dehumidification of air

ABSTRACT

Air may be dehumidified in an apparatus, comprising, in combination, a primary heat exchanger provided with a variable volume primary coolant for environmental cooling for thereby dehumidifying air in process, a secondary heat exchanger provided with a circulating secondary coolant for cooling the primary coolant, and means for controlling the circulation of the secondary coolant according to volume variations of the primary coolant. Suitable primary coolants include admixtures of a suitable liquid, for instance water, or an aqueous solution of a freezing point depressant, and ice. Volume variations of the primary coolant occur as ice in the admixture melts and liquid freezes and accumulates as ice.

United States Patent [191 Hirano 1 Jan. 21, 1975 DEHUMIDIFICATION OF AIR[76] Inventor: Itsuro Hirano, 2-3-34-1905, Mita, Wye

Minatmku, Tokyo Japan Attorney, Agent, or Fzrm--Blum, Moskovuz, Fr1edman& Kaplan [22] Filed: Oct. 2, 1973 [21] Appl. No.: 402,670 57 R C Air maybe dehumidified in an apparatus, comprising, [30] Forelgn ApphcatloPnomy Data in combination, a primary heat exchanger provided Oct. 2,1972 Japan 47-97985 with a variable volume primary coolant forenvironmental cooling for thereby dehumidifying air in pro- [52] US. Cl62/93, 62/150, 62/177, cess, a secondary heat exchanger provided with acir- 2/283, 62/317, 62/406 culating secondary coolant for cooling theprimary [51] Int. Cl. F25d 17/06 coolant, and means for controlling thecirculation of Field of Search the secondary coolant according to volumevariations 371, 1 of the primary coolant. Suitable primary coolantsinclude admixtures of a suitable liquid, for instance wa- [56]References Cited ter, or an aqueous solution of a freezing point depres-UNITED STATES PATENTS sant, and ice Volume variations of the primarycool- 2,000,467 5/1935 Lindseth 165/26 am Occur as ice in the admixturemelts and quid 2,720,084 10/1955 Hailey freezes and accumulates as3,050,954 8 1962 R0 se..... 3,105,362 10/1963 Goiild 62/126 12 Glam, 2D'awmg F'gures DEHUMIDIFICATION OF AIR BACKGROUND OF THE INVENTION.

This invention relates to a method and apparatus for dehumidifying airfor the drying thereof.

It has been known to cool air or compressed air for dehumidificationthereof. According to conventional processes, air is usually cooled toC. or lower, with the concomitant unsatisfactory result that air pathoutlets for the processed air may freeze over, whereby the flow of airin process may be disturbed. Therefore, dehumidification processes inwhich air is cooled to 0 C. or lower are generally unsatisfactory. Thereis a longfelt, but heretofore unsatisfied need for a dehumidificationprocess and apparatus wherein air in process may be cooled near butabove 0 C. for effective drying. In a dehumidification process whereinair in process may be cooled within that optimal temperature range,larger quantities of condensate may be extracted therefrom for drier airthan achieved with heretofore known processes of the type described andconcomitantly, air outlet freeze-over may be eliminated.

It is, therefore, a principal object of this invention to provide amethod and apparatus for dehumidifying air, wherein the temperature ofprocessed air is near but above 0 C.

It is another object of the present invention to provide a method andapparatus for dehumidifying air which performs satisfactorily at lowerthan the usual energy input levels and decreases the strain upon alreadyoverextended available energy sources.

It is yet another object of the instant invention to provide adehumidification method and apparatus for drying air wherein thetemperature of air in process may be regulated within substantiallyincremental limits.

SUMMARY OF THE INVENTION Generally speaking, in accordance with thisinvention, air may be dehumidified in an apparatus, comprising, incombination, a primary heat exchanger provided with a variable volumeprimary coolant for environmental cooling for thereby dehumidifying airin process, a secondary heat exchanger provided with a circulatingsecondary coolant for cooling the primary coolant, and means forcontrolling the circulation of the secondary coolant according to volumevariations of the primary coolant. Suitable primary coolants includeadmixtures ofa suitable liquid, for instance water, or an aqueoussolution of a freezing point depressant, and ice. Volume variations ofthe primary coolant occur as ice in the admixture melts and liquidfreezes and accumulates as ice.

This invention utilizes heat capacity of the primary coolant for latentheat at its freezing point. The volume thereof must increase duringfreezing, and the temperature thereof must remain constant duringfreezing. Any fluid or admixture with these properties may be employedherein as the primary coolant. For instance, water or aqueous solutionsof selected freezing point depressants such as NaCl or CaCl may besatisfactorily employed as the primary coolant for this invention.Volume variations of the primary coolant, caused by cyclical freezingand melting of parts thereof, are directly utilized for selectivelycompressing an expansible member, for instance a bellows, forselectively actuating electric circuits for pumping the secondarycoolant,

for indicating states of the primary coolant, and for indicatingoverload.

In an alternative embodiment, volume variations of the primary coolantare utilized directly or through an intermediary gas, for instance airand preferably nitrogen, confined with the primary coolant in aclosed-vessel. A pressure switch for controlling the flow of thesecondary coolant is driven by pressure variations corresponding tovolume variations of the primary coolant or intermediary gas formaintaining the-quantity of the ice admixed with primary coolant betweenselectively prescribed'maximum and minimum levels correspondingtopreselectedupper and lower pressure switch limits.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the several steps and the relationofone or more of such steps with respect to each of the others, and theapparatus embodying features ofconstruction, combinations of ele mentsand arrangement of parts which are adapted to effect such steps, allexemplified in the following detailed disclosure, and the scope of theinvention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawings, in which:

FIG. 1 is a schematic representation of one type of apparatus fordehumidification of air-constructed in accordance with the invention;and

FIG. 2 is a schematic representation of another type of apparatus, alsoconstructed in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, anadiabatic, pressure resisting closed vessel 10 is filled with a primarycoolant, comprising water or a suitable aqueous solution of freezingpoint depressant, admixed with a small quantity of a suitable gas, suchas air and preferably N When the volume of the closed vessel 10 isappreciably large, the quantity of primary coolant deposited therein maybe commensurately reduced by the gas addition to the vessel and volumevariations of the primary coolant cause corresponding volume variationsin the gas.

A coiled pipe 11 is arranged interiorly of vessel I0 for forming aprimary heat exchanger, and first and second portions thereof extendexteriorly for providing an inlet 12 and an outlet 13 therefor. Onoutlet 13, a drain valve 14 is mounted.

Another coiled pipe 15 is also arranged interiorly of vessel 10 forforming a secondary heat exchanger, and a portion thereof extendsexteriorly of vessel 10 for connecting the pipe I5 to a source of asecondary coolant, such as a refrigerator (not shown). v

The adiabatic, pressure resisting wall of the vessel I0 has anexpansible member 16, such as bellows, which responds to volumevariations of the primary coolant and an end thereof I7 is displaceableaccording to volume variations. Displaceable end 17 may be displacedalong electrical contacts 18, I9 and 20. Three circuits including thethree contacts 18, I9 and 20 and also three lamps 21, 22 and 23, are,respectively, adapted to be energized by a source 24. The lamp 21 is ayellow lamp, which lights when there is an overload. The lamp 22 is ablue lamp, which lights when the refrigerator opcrates and secondarycoolant circulates, for operating the secondary heat exchanger. The lamp23 is a red lamp, which lights when the refrigerator is not operatingand secondary coolant is not flowing, but the secondary heat exchangeris still in operation. When yellow lamp 21 or blue lamp 22 are lit, anelectric motor 26 is energized by another power source 27 for driving apump 31 which pumps secondary coolant through coiled pipe 15 of thesecondary heat exchanger. When the red lamp 23 is lit, anelectromagnetic switch 25 is actuated for deenergizing the motor 26 and,in turn, the pump 31 for automatically avoiding excessive cooling.

The primary coolant confined inside the closed vessel 10 is continuouslyagitated by a stirrer 28 driven by a motor 33 for maintaining theprimary coolant at a substantially uniform temperature.

in operation, the primary coolant has been cooled to C. or near 0 C.,and mixed with ice. Air to be dried, which may be compressed air, isadmitted into the coiled pipe 11 of the primary heat exchanger throughinlet 12 for cooling to near 0 C., by the primary coolant, and forseparation from water suspended therein. Thus, only cold air outletsthrough outlet 13 and condensate is drawn off through the drain valve14.

The primary coolant is confined within adiabatic, pressure resistingclosed vessel either with or without a small quantity of air which whenpresent accumulates inside the expansible member 16 for transmittingvolume variations of the primary coolant to displaceable end 17 thereofand volume variations of the primary coolant are transmitted directly orthrough the intermediate air to displaceable end 17 which respondsaccordingly. Mounted on the top wall of closed vessel 10 are a pressurerelief means 29 and a pressure gauge 30, for adjusting the maximumpressure of the primary coolant. The relief means 29 and the pressuregauge 30 may be of a conventional construction well-known to theart-skilled.

Usually the temperature of the inlet air for processing is higher than 0C., and therefore the temperature of the primary coolant tends to beelevated at the primary heat exchanger. Because the primary coolant ismixed with ice, it has a substantial heat capacity and a substantialresistance to temperature elevations. While the secondary coolantcirculates, the quantity of ice in the primary coolant increases and theoverall volume of the primary coolant increases for thereby displacingend 17 of expansible member 16 from its connection with contact 18 tocontact with contact 19. Thus, yellow lamp 21 goes out and blue lamp 22ignites. This indicates that, at this instant, dehumidification of theinput air is ready to be effected and started with the primary coolant,and is the desirable normal condition. In the embodiment, the primarycoolant includes about percent of ice at this instant.

When the primary coolant is excessively cooled by the secondary coolantso that, in an embodiment, about 50 percent of the water of the confinedprimary coolant is frozen, it is further expanded. In accordance withthe expansion, end 17 of expansible member 16 is displaced from contact19 moved to contact 20 and therefore blue lamp 22 goes out and the redlamp 23 lights. Simultaneously therewith, electromagnetic switch 25 isactuated for breaking motor 26 for thereby interrupting recirculation ofthe secondary coolant. In general, fluctuation between conditions wherethe blue lamp 22 lights and where red lamp 23 lights is to be considereda normal condition.

If yellow lamp 21 ignites while the secondary heat exchanger isoperating at full capacity, that signifies that the dehumidifyingcapacity of the apparatus is short, and therefore, it is necessary toreduce air input. This condition may occur when the volume ratio of iceto primary coolant is less than 20 percent, whereby the reduced volumeof primary coolant deflates expansible member 16 and end 17 thereofcontacts with contact 18 of yellow lamp 21.

The primary coolant to be confined within adiabatic, pressure resistingclosed vessel 10 may be water or a selected aqueous solution of afreezing point depressant. Suitable freezing point depressants includesodium salts such as NaCl, calcium salts such as CaCl and the like. Thefreezing point of the primary coolant may be adjusted from 0 C. to lOC., by the freezing point depressant. When the adjustment is made andwhen the temperature of the output air at outlet 13 is near 0 C., thetemperature gradient between the interior of the coiled pipe 11 and theprimary coolant within the closed vessel 10 steepens. By virtue thereof,the heat transferring surface may be reduced for economizing theconstruction cost of the apparatus.

Reference is now made to FIG. 2 which illustrates another embodiment ofthe invention. Air for drying is admitted through inlet 12 into a waterseparator 48 and is cooled thereby. The cooled air is admitted into aheat exchanger 49, wherein the cooled input air is further cooled by theoutput air directed to the outlet 13. The twice pre-cooled air is thenadmitted into an air chamber 47 provided with a coiled pipe 45interiorly arranged therein constituting the primary heat exchanger andthe precooled air is substantially cooled and dehumidified by thisprimary heat exchanger. Condensate drainage occurs counterflow to theair in process for further cooling the latter and condensate iscollected in water separator 48 which is provided with a drain valve 14for expelling the condensate out of the apparatus.

The primary coolant is water in this embodiment and it is circulatedthrough coiled pipe 45 for forming the primary heat exchanger, andintroduced into an adiabatic, pressure resisting closed vessel 41. Forrecirculating the primary coolant, coiled pipe 45 is connected with theclosed vessel 41 by connecting pipes 43 and 46, and the connecting pipe43 is provided with a pump 44.

Adiabatic, pressure resisting closed vessel 41 is provided thereon witha pressure resisting air vessel 42 provided with a pressure relief means29 and a pressure gauge 30. There is arranged inside the adiabatic,pressure resisting closed vessel 41 a coiled pipe 15 for recirculatingthe secondary coolant from the refrigerator (not shown), which therebyconstitutes the secondary heat exchanger inside the closed vessel 4]. Inthis embodiment, the secondary coolant is a Freon gas. A control switch35 is also connected on pressure resisting air vessel 42 and controlsthe flow of the recirculating secondary coolant in response to the airpressure in the pressure resisting air vessel 42 or volume variations ofthe primary coolant, for maintaining the volume of ice contained in theprimary coolant between about 20 percent and 50 percent. As the controlswitch 35, it is preferred to use a pressure having an upper and lowerlimit, which may be set in such a manner that the limits correspond tothe maximum and the minimum pressures for maintaining the volume of icewithin the above-mentioned range.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above composition of matterwithout departing from the spirit and scope of the invention, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:

1. An apparatus for dehumidifying air, comprising, in combination, aprimary heat exchanger for dehumidifying air, a primary coolant forcooling said primary heat exchanger, a secondary heat exchanger forcooling said primary coolant, a secondary coolant for cooling saidsecondary heat exchanger, means for controlling circulation of saidsecondary coolant through said secondary heat exchanger responsive tovolume variations of said primary coolant, an adiabatic, pressureresisting closed vessel for housing said primary heat exchanger, saidprimary heat exchanger including an air chamber for circulating air inprocess, a heat exchanging element being arranged in said air chamberfor recirculating said primary coolant, and means for recirculating saidprimary coolant through said heat exchanging element; and another heatexchanger arranged in said air chamber for precooling air to be treatedwith treated air.

2. The combination of claim 1 wherein said primary coolant comprises anadmixture of water or an aqueous solution of a freezing pointdepressant, and ice.

3. The combination of claim 1 wherein said means is directly responsiveto volume variations of said primary coolant.

4. The combination of claim 1 including a small quantity of gas foractuating said means; said gas being responsive to volume variations ofsaid primary coolant for thereby actuating said means.

5. The combination of claim 4 wherein said gas is nitrogen.

6. The combination of claim 1 wherein said primary heat exchangercomprises a heat exchanger having air inlet and outlet portions forcirculating air for processing there through and including an adiabatic,pressure resisting closed vessel, said vessel housing said primarycoolant, said heat exchanger being mounted in said vessel with saidinlet and outlet portions extending exteriorly thereof.

7. The combination of claim 1 and wherein said means for controllingcirculation of said secondary coolant comprises an expansible memberconnected to said vessel, said expansible member being responsive tovolume variations of said primary coolant caused by cyclically freezingand melting a portion thereof and including a circuit actuable by saidexpansible member for interrupting circulating of said secondary coolantthrough said another heat exchanger.

8. The combination of claim 7 wherein said circuit in a closed conditionignites an indicator lamp.

9. The combination of claim I wherein said secondary heat exchangercomprises an adiabatic, pressure resisting closed chamber, means forcirculating said primary coolant through said chamber for cooling saidprimary coolant and a heat exchanging element arranged in said chamberfor carrying circulating secondary coolant for cooling said chamber,said secondary coolant being recirculated through said heat exchangingelement and including a refrigerant source for cooling said secondarycoolant.

10. The combination of claim 9 wherein said controlling means comprisesa pressure switch having an upper and lower limit adapted for,respectively, representing maximum and minimum optimal ice contents forsaid primary coolant, for controlling secondary coolant recirculationfor thereby maintaining ice content between said optimal maximum andminimum limits.

1]. The combination of claim 1 including a water separator forcollecting condensate extracted from air in process, said waterseparator being arranged below said another heat exchanger, and meansfor connecting said water separator and said air chamber for carryingcondensate therefrom to said water separator.

12. A method for dehumidfying air comprising cooling said air with aprimary coolant, confining said primary coolant within a sealed pressurevessel, circulating said primary coolant through a primary heatexchanger, cooling said primary coolant with a secondary coolant,selectively recirculating said secondary coolant through a secondaryheat exchanger and a refrigerant source, and controlling saidrecirculation of said secondary coolant according to control responsestransmitted at predetermined primary coolant volume variation levels formaintaining an ice volume in said primary coolant of between 20 and 50percent; said primary coolant being an admixture of water or an aqueoussolution of a freezing point depressant, and ice.

1. An apparatus for dehumidifying air, comprising, in combination, aprimary heat exchanger for dehumidifying air, a prImary coolant forcooling said primary heat exchanger, a secondary heat exchanger forcooling said primary coolant, a secondary coolant for cooling saidsecondary heat exchanger, means for controlling circulation of saidsecondary coolant through said secondary heat exchanger responsive tovolume variations of said primary coolant, an adiabatic, pressureresisting closed vessel for housing said primary heat exchanger, saidprimary heat exchanger including an air chamber for circulating air inprocess, a heat exchanging element being arranged in said air chamberfor recirculating said primary coolant, and means for recirculating saidprimary coolant through said heat exchanging element; and another heatexchanger arranged in said air chamber for precooling air to be treatedwith treated air.
 2. The combination of claim 1 wherein said primarycoolant comprises an admixture of water or an aqueous solution of afreezing point depressant, and ice.
 3. The combination of claim 1wherein said means is directly responsive to volume variations of saidprimary coolant.
 4. The combination of claim 1 including a smallquantity of gas for actuating said means; said gas being responsive tovolume variations of said primary coolant for thereby actuating saidmeans.
 5. The combination of claim 4 wherein said gas is nitrogen. 6.The combination of claim 1 wherein said primary heat exchanger comprisesa heat exchanger having air inlet and outlet portions for circulatingair for processing there through and including an adiabatic, pressureresisting closed vessel, said vessel housing said primary coolant, saidheat exchanger being mounted in said vessel with said inlet and outletportions extending exteriorly thereof.
 7. The combination of claim 1 andwherein said means for controlling circulation of said secondary coolantcomprises an expansible member connected to said vessel, said expansiblemember being responsive to volume variations of said primary coolantcaused by cyclically freezing and melting a portion thereof andincluding a circuit actuable by said expansible member for interruptingcirculating of said secondary coolant through said another heatexchanger.
 8. The combination of claim 7 wherein said circuit in aclosed condition ignites an indicator lamp.
 9. The combination of claim1 wherein said secondary heat exchanger comprises an adiabatic, pressureresisting closed chamber, means for circulating said primary coolantthrough said chamber for cooling said primary coolant and a heatexchanging element arranged in said chamber for carrying circulatingsecondary coolant for cooling said chamber, said secondary coolant beingrecirculated through said heat exchanging element and including arefrigerant source for cooling said secondary coolant.
 10. Thecombination of claim 9 wherein said controlling means comprises apressure switch having an upper and lower limit adapted for,respectively, representing maximum and minimum optimal ice contents forsaid primary coolant, for controlling secondary coolant recirculationfor thereby maintaining ice content between said optimal maximum andminimum limits.
 11. The combination of claim 1 including a waterseparator for collecting condensate extracted from air in process, saidwater separator being arranged below said another heat exchanger, andmeans for connecting said water separator and said air chamber forcarrying condensate therefrom to said water separator.
 12. A method fordehumidfying air comprising cooling said air with a primary coolant,confining said primary coolant within a sealed pressure vessel,circulating said primary coolant through a primary heat exchanger,cooling said primary coolant with a secondary coolant, selectivelyrecirculating said secondary coolant through a secondary heat exchangerand a refrigerant source, and controlling said recirculation of saidsecondary coolant according to control responses transmitted atpredetermined primary coolant volume variation levels for maintaining anIce volume in said primary coolant of between 20 and 50 percent; saidprimary coolant being an admixture of water or an aqueous solution of afreezing point depressant, and ice.